The Decktet is an alternative deck of cards created by P.D. Magnus. Numerous card and Euro-style games have been designed for the Decktet; you can find about 130 of them at the Decktet wiki, and about 85 of them also have entries at BoardGameGeek. As originally released, the Decktet had 36 cards. These cards had one or two of the six Decktet suits: Moons, Suns, Waves, Leaves, Wyrms, and Knots). There is one Ace of each suit, one Crown of each suit, and three cards in each rank from 2 to 9. Numbered cards have two suits each, in a fixed but not regular pattern.
Later releases added the four Pawns, four Courts, and The Excuse. These are referred to as the extended deck in rules, and, while they are a standard part of the deck today, they are sometimes omitted from games or included only in variants. The Excuse is a sort of Decktet joker with no suits. Pawns and Courts have three suits each, again in no particular pattern. When ordering cards by rank, Pawns and/or Courts are inserted between the nines and the Crowns, in that order.
The original art was released under a CC license and printed-and-played extensively, and has been incorporated into other online Decktet games. (Only suit and rank symbols are used at Abstract Play.) It is also possible to buy a copy of the original Decktet and/or an equivalent set with new art and names (but the same suits); see the Decktet site for more details.
At Abstract Play, the Excuse is represented by a zero. Other cards use the standard Decktet abbreviations: Aces are represented by their suit symbol alone, and the remaining cards by their rank or symbol plus their suit(s). The symbols are: a single pawn for Pawns, a pair of pawns for Courts, and a crown for Crowns. Most cards also have names (e.g., the Borderlands) and types (personality, event, and/or location), but these are not in use (yet) at Abstract Play.
In the chat log, cards may be logged using an abbreviated style, <rank><suit?><suit?><suit?>, where the ranks are 0, 1, 2-9, P, T, N (for the Excuse, Aces, ranks 2-9, Pawns, Courts, and Crowns, respectively), and the suit initials are M, S, V, L, Y, K (for Moons, Suns, Waves, Leaves, Wyrms, and Knots, respectively).
For example, PMSL stands for the Pawn of Moons, Suns, and Leaves, and 8VL represents the 8 of Waves and Leaves.